We have already reported that a charge-transporting thin film obtained from an organic solvent-based charge-transporting varnish making use of a charge transport material made of a low molecular weight oligoaniline compound exhibits excellent electroluminescent device characteristics (see Patent Document 1: JP-A 2002-151272).
In the charge-transporting varnish of Patent Document 1, the low molecular weight oligoaniline compound serving as a charge transport material has a structure of the same repeating units in the molecule and has such a nature that a more elongated conjugated system results in a higher degree of coloration and also in a greater absorption in the visible region when formed as a charge-transporting thin film.
It is known that the coloration of a charge-transporting thin film lowers the color purity and color reproducibility of an organic electroluminescent (hereinafter referred to as organic EL) device.
In addition, the coloration presents a problem in many full color techniques of organic EL displays such as of tricolor luminescence, white color luminescence, and color conversion and becomes a considerable obstacle in the stable manufacture of organic EL devices.
Therefore, it is desirable that the charge-transporting thin film of an organic EL device be high in transmittance in the visible region and high in transparency.    Patent Document 1: JP-A 2002-151272